Head coach Antonio Conte says Chelsea need David Luiz to play against Atletico Madrid with a broken wrist.
Luiz sustained the injury in Sunday's goalless draw with Arsenal when he clattered into the advertising hoardings at the end of the first half.
The Brazil defender continued in the second half until he was dismissed after 87 minutes for a reckless tackle on Sead Kolasinac which saw him given a three-game suspension.
Luiz missed Wednesday night's 5-1 Carabao Cup win over Nottingham Forest and will also be ineligible for the Premier League clashes with Stoke and, crucially, Manchester City.
But Conte expects Luiz to play at Atletico in the Champions League next Wednesday.
"He must be okay," Conte said.
"David is an important player for us. For sure he will be ready for the game against Atletico Madrid."
In Luiz's absence, Chelsea's youngsters impressed against Championship Forest.
Michy Batshuayi scored a hat-trick, while Kenedy and the impressive Charly Musonda were also on target for Chelsea. Tendayi Darikwa scored a late consolation.
Eden Hazard delighted on his first start of the season after his broken ankle, while Conte assessed the Chelsea youth.
Chelsea academy graduates Musonda, Andreas Christensen, Jake Clarke-Salter and Dujon Sterling featured, while Ethan Ampadu became the first Chelsea player born this millennium, a week after his 17th birthday.
Conte suggested he could field a similar squad in the fourth round against Everton.
Conte said: "We are a great club, for this reason every competition is important to us. If we answer like this tonight, why not continue to give the opportunity to these players?"
Kenedy's Blues career looked like it could be coming to an end when he was sent home from the pre-season tour to Asia following some ill-advised social media posts on China. He apologised and has been reintegrated into the squad.
The Brazilian scored Chelsea's first and his first goal since March 2016 when he ghosted behind the Forest defence to meet Antonio Rudiger's cross with a side-footed shot that beat goalkeeper Stephen Henderson.
Conte was asked about the pre-season controversy, but side-stepped questions on it, preferring to focus on Kenedy's performance.
"Kenedy played very well," Conte said.
"He's working very well, he's working a lot. When there will be the opportunity, a new chance, he must exploit it."
Forest boss Mark Warburton was frustrated with his side's defending.
"You can't give away soft goals. It's as simple as that," Warburton said.